The present invention relates to a method for introducing fuel and/or thermal energy into a gas stream flowing to a catalytic reactor. Additionally, the present invention relates to a device for executing the method.
Supplying catalytic reactors with thermal energy (for example, heating catalysts in an exhaust gas branch or catalytic burners in the area of a gas generating system for generating hydrogen-containing gas for a fuel cell system) must occur particularly during the starting phase to achieve an appropriate starting temperature, in particular in mobile application situations, as quickly as possible.
For this, catalytic reactors are generally supplied (1) with thermal energy that is generated for example during combustion or similar processes; and/or (2) with a fuel directly, which can occur both during the starting phase and during normal operation, i.e. with a catalytic reactor that has reached an operating temperature, and which releases thermal energy in the reactor.
The present invention is based on an object of creating a method that enables the supply of fuel and/or thermal energy into a gas stream flowing to the catalytic reactor in a very simple, robust, and space-saving manner with regard to its control and device requirements.
This object is achieved according to preferred embodiments of the present invention.
The method exhibits the particular advantage that the gas stream flowing to the catalytic reactor, for example, (1) air, which flows to a catalytic burner, or (2) exhaust gas of an internal combustion engine, which flows after the starting phase of the internal combustion engine to an exhaust gas catalyst in the form of a heating catalyst and is still cold and contains oxygen, is guided through an external chamber and an internal chamber. The interior chamber is supplied with fuel, which is burned in a starting phase of the still cold catalytic reactor to supply thermal energy to the catalytic reactor through the generated hot exhaust gases. The gas flowing to the catalytic reactor overall would not form an ignitable mixture with a conventional burner design with the appropriately metered quantity of fuel. Due to the fact, however, that a certain quantity of gas flows through the exterior chamber and another partial quantity of the gas flows through the interior chamber, an ignitable mixture can be created in the interior chamber so that a combustion process can take place, without having to reduce the overall amount of gas that is supplied to the catalytic burner at that time during the operation.
Additionally, excessive warming of the exterior chamber is prevented with a relatively cold gas that flows through the area of the exterior chamber and around the interior chamber. A component in which the method takes place can be installed into a system (e.g., a gas generating system for a mobile fuel cell system) without further thermal insulation or similar measures in a very space-saving and inexpensive manner.
During the subsequent course of the method when the catalytic reactor has reached its conventional normal operation and is running at its operating temperature, fuel that may be required for the operation of the catalytic reactor can be vaporized in the interior chamber. The energy required for this process can be derived from the gas stream flowing through the two chambers.
In a particularly favorable embodiment of the present invention, an additional gas stream can be introduced into the area of the exterior chamber, which contains additional fuels. These fuels can then be burned catalytically in the area of the exterior chamber. The generated thermal energy can be used for the vaporization of the fuel that has been introduced into the interior chamber.
An alternative embodiment of the method provides a feature so that the gas stream flowing into the catalytic reactor already carries fuels with it. The gas stream can be, for example, a low-oxygen reformate or educt stream.
The gas stream, as described above, flows through the burner system having an exterior chamber and an interior chamber. Only in the area of the interior chamber is an oxygen-containing medium, which can be air, introduced. In this area, a flame can be ignited due to low flow speed. Due to the stable flame in the interior chamber, a combustion process can be achieved that can take place both superstoichiometrically and substoichiometrically, depending on the requirements.
By mixing the flame with a cold portion of the gas stream that flows through the exterior chamber, an inflow temperature that is compatible for the catalytic reactor is enabled, which is far below the exhaust gas temperature of the open flame. Additionally, by cold gas flowing around the tube element, which can form the interior chamber, the loss of heat in such a device is minimized. Thermal stress from neighboring components (e.g., when used in a gas generating system) is eliminated. Otherwise, the same features that have already been mentioned apply here as well.
An appropriate device for performing the described method has the design of a two-tube burner. The exterior chamber and the interior chamber are formed by two tube elements that are arranged inside one another. As required pursuant to the above method, the tubes are open in the flow direction of the gas, i.e. here on the front ends, so that the gas stream flowing into the device is divided between the two chambers in dependency upon the cross-section of the two tube elements.
In a beneficial embodiment of the device, the area of walls of the interior chamber facing the exterior chamber can be equipped with several components that enlarge the surface, which in a very favorable development additionally contain a catalytic coating.
Thus, when additional fuel is burned catalytically in the area of the exterior chamber, this combustion process occurs directly on the appropriate component, which can have the design, for example, of a fin or rib. The generated thermal energy is released with the appropriate fuel that is supposed to be vaporized via thermal conduction to the walls of the interior chamber and from there through heat transmission to the gas flowing through the interior chamber.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the present invention when considered in conjunction with the accompanying drawings.